Most systems for producing energy locally, such as by converting solar energy or wind energy to electricity, produce electrical power in the form of DC current at a voltage of, for example, 12 volts. This DC current output of the power generator is then converted to AC current and supplied to power the associated building via the standard AC electrical system of the building. Where there is no power usage in the building and there is an excess of generated DC power, the DC current may be used directly to charge a battery storing the power for future use. When power is need in the building this battery discharges, providing DC current, which is also converted to AC current and transmitted as AC current to the standard AC electrical system of the building.
As is well known, buildings in most of the world are supplied with electrical power in the form of AC current sent to sockets in the walls of buildings. These sockets are usually standard sockets for the given country. For example in the U.S., sockets are usually in the form of two parallel slots. One contact in the socket connects to one pole of an AC current supply and the other contact in the socket connects with a complementary pole of the AC current supply. These poles of the AC current usually referred to as the phase and the other the neutral.
AC power is obtained at the socket by plugging a standard two-prong plug into the socket. The two-prong plug has two rectangular AC connection prongs that are inserted into the two slots or recesses in the socket so as to make contact with springing metal contacts that supply AC current to those prongs. As a result, a circuit with flowing AC current is formed by a device electrically connected between the two prongs.
As is also well known, in addition to such a standard two-plug AC plug and socket arrangement, the socket may have a third recess or slot, usually circular in cross section, that receives a third cylindrical prong of a standard three-prong plug, and contacts this third prong and connects it to a grounded connection.
At the same time, more and more devices now rely on DC current for operation, including computers, computer speakers, lighting, televisions, cordless telephones, answering machines, video games, cordless tools, and many other devices that rely on a DC power source to operate. These devices normally derive power from a standard AC plug that takes AC current at the local voltage (in the U.S. 110 volts) and sends it through an AC/DC converter that converts to 110 v. AC current to a DC current at a voltage appropriate for the associated device. Presently about 6% of the U.S. power consumption is attributable to such low-power DC devices.
Where the device is used in a building with its own DC electrical power generation, the result is that the DC current from the solar or windmill or other generator is converted to DC current, with a consequent loss of 10 to 15% of total power to the conversion. A subsequent conversion of the AC to DC, depending on the type of transformer or converter used, results in an additional loss of 30 to 70% of the power of the AC. As a result, the use of a DC electrical device in a building powered by a DC generator such as a photoelectric panel system or a wind power generator is extremely inefficient relative to the solar or wind energy captured.
Transmission of both AC and DC power to the various sockets of the building is not readily possible because sockets as presently configured provide only two slots for AC power and possibly a third circular recess providing a ground connection. Changing this configuration is undesirable because many devices rely on AC current and have plugs configured to use the standard two- or three-prong sockets. Supplying DC power to the standard socket for use with a DC power device with a standard AC plug would potentially result in confusion and damage if a DC device were plugged in to an AC socket.